1. Field of the Invention
The invention relates generally to the field of digital signal modulation and coding. More particularly, the invention relates to a low rate codec using convolutional and block coding with a phase shift keying constellation.
2. Description of the Related Art
Presently in transmitting and receiving digital data across noisy channels, it is difficult to find a suitable compromise between adequate bandwidth efficiency and adequate error correction capabilities. With full error correction coding, the bit rate becomes too low or the bandwidth requirements too high. With only modest error correction coding, much of the transmitted signal can become unrecoverable at the receiver. In order to provide a robust communications link, the data should be recoverable and yet bandwidth limitations should be honored.
The present invention provides a unique combination of error correction coding that allows for a very robust communication link in noisy channels. It is suitable for any kind of digital signal processing systems but is particularly suitable for wireless digital data communications systems.
A method and apparatus are provided that yields bandwidth efficient low bit rate communication of digital signals in a noisy channel. According to one aspect of the present invention, the invention includes demultiplexing a received input bit stream to divide it into a first block and a second block, convolutionally coding the first block, block coding the second block, mapping the convolutionally coded first block to a sequence of three-bit symbols, so that the bits of the convolutionally coded first block make up one bit of each three-bit symbol, mapping the block coded bits of the second block to the sequence of three-bit symbols, so that the bits of the block coded second block make up two bits of each three-bit symbol, and mapping the three-bit symbols to a phase shift keyed constellation.